count() for continuous substrings in python

Question

Why does the following program return 1 instead of 2 in python?

print "abcdcdc".count("cdc")

The substring cdc appears in two places(one starting at index 2 and the another starting at index 4). How exactly does the count() work?

Answer 1

May I refere you to

https://docs.python.org/3.4/library/stdtypes.html?highlight=count#str.count

str.count(sub[, start[, end]])

Return the number of non-overlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.

Answer 2

count only returns 1 because the value cdc overlaps itself.

abcdcdc
  |-|
    |-|

To get a value of 2, you need two non-overlapping instances of cdc or utilize a regex:

import re
len(re.findall('(?=cdc)', 'abcdcdc'))

Answer 3

If you would like to count the total number of occurrences with overlap, you can do this with re module:

import re
text = 'abcdcdc'
len(re.findall('(?=cdc)', text))
>>> 2

Answer 4

Because count() returns the number of non-overlapping occurrences of substring. See Docs.